Improved diagnosis of early kidney allograft dysfunction by ultrasound with echo enhancer--a new method for the diagnosis of renal perfusion

Factors influencing the time-intensity curve analysis of contrast-enhanced ultrasound in kidney transplanted patients: Toward a standardized contrast-enhanced ultrasound examination

Background

Time-intensity curve analysis (TIC analysis) based on contrast-enhanced ultrasound (CEUS) provides quantifiable information about the microcirculation of different tissues. TIC analysis of kidney transplantations is still a field of research, and standardized study protocols are missing though being mandatory for the interpretation of TIC parameters in the clinical context. The aim of this study was to evaluate the impact of different sizes and forms of regions of interest (ROIs) on the variance of different TIC parameters and the level of interoperator variance between the different ROI methods in kidney transplantations.

Methods

In 25 renal transplanted patients, 33 CEUS of the transplanted kidney were performed, and TIC analysis with ROIs sized 5 mm2 (ROI5), 10 mm2 (ROI10), and ROIs circumscribing the outlines of anatomical regions (ROI Anat ) were analyzed based on CEUS examination. The TIC analysis was repeated by a second independent operator for ROI5 and ROI Anat .

Results

Statistical analysis revealed significant differences between TIC parameters of different ROI methods, and overall, the interoperator variance was low. But a greater ROI surface (ROI10) led to higher values of the intensity parameters A and AUC compared with ROI5 (p < 0.05). The difference in the ROI form led to high variation of certain TIC parameters between ROI5 and ROI Anat in the myelon [intraclass correlation coefficient (A, ICC = 0.578 (0.139-0.793); TIC parameter (TTP); and ICC = 0.679 (0.344-0.842) (p < 0.05)]. A mean variation of 1 cm of the depth of ROI5 in the cortex did not show significant differences in the TIC parameters, though there was an impact of depth of ROI Anat on the values of TIC parameters. The interoperator variance in the cortex was low and equal for ROI5 and ROI Anat , but increased in the myelon, especially for ROI Anat . Furthermore, the analysis revealed a strong correlation between the parameter AUC and the time interval applied for the TIC analysis in the cortex and myelon (r = 0.710, 0.674, p < 0.000).

Conclusion

Our findings suggest the application of multiple ROIs of 5 mm2 in the cortex and medulla to perform TIC analysis of kidney transplants. For clinical interpretation of AUC, a standardized time interval for TIC analysis should be developed. After the standardization of the TIC analysis, the clinical predictive value could be investigated in further studies.

Quantitative contrast-enhanced ultrasound for the differentiation of kidney allografts with significant histopathological injury

OBJECTIVE

To identify specific quantitative contrast-enhanced ultrasound (CEUS) parameters that could distinguish kidney transplants with significant histopathological injury.

METHODS

Sixty-four patients were enrolled in this prospective observational study. Biopsies were performed following CEUS and blood examination.

RESULTS

28 biopsy specimens had minimal changes (MC group), while 36 had significant injury (SI group). Of these, 12 had rejection (RI group) and 24 non-rejection injury (NRI group). In RI and NRI groups, temporal difference in time to peak (TTP) between medulla and cortex (ΔTTPm-c) was significantly shorter compared to the MC group (5.77, 5.92, and 7.94 s, P = 0.048 and 0.026, respectively). Additionally, RI group had significantly shorter medullary TTP compared to the MC group (27.75 vs. 32.26 s; P = 0.03). In a subset of 41 patients with protocol biopsy at 1-year post-transplant, ΔTTPm-c was significantly shorter in the SI compared to the MC group (5.67 vs. 7.67 s; P = 0.024). Area under receiver operating characteristic curves (AUROCs) for ΔTTPm-c was 0.69 in all patients and 0.71 in patients with protocol biopsy.

CONCLUSIONS

RI and NRI groups had shorter ΔTTPm-c compared to the MC group. AUROCs for both patient groups were good, making ΔTTPm-c a promising CEUS parameter for distinguishing patients with significant histopathological injury.

Evaluation of the Graft Kidney in the Early Postoperative Period: Performance of Contrast-Enhanced Ultrasound and Additional Ultrasound Parameters

OBJECTIVES

To evaluate the various quantitative parameters of Doppler ultrasound, contrast-enhanced ultrasound (CEUS), and shear wave elastography (SWE) of graft kidneys in the early postoperative period and to explore their utility in the diagnosis of parenchymal causes of graft dysfunction.

METHODS

In this ethically approved study, consecutive patients who underwent renal transplantation from March 2017 to August 2018 were recruited, and those with urologic or vascular complications and those who denied consent were excluded. All patients underwent ultrasound with Doppler, SWE, CEUS (using sulfur hexafluoride), and renal scintigraphic examinations 3 to 10 days after transplantation. A composite reference standard was used, including the clinical course, renal function test results, urine output, and histopathologic results for graft dysfunction. Cortical SWE values, quantitative CEUS parameters (generated from a time-intensity curve), and their ratios were analyzed to identify graft dysfunction and differentiate acute tubular necrosis (ATN) from acute rejection (AR).

RESULTS

Of the 105 patients included, 19 developed graft dysfunction (18.1%; 12 ATN, 5 AR, and 2 drug toxicity) in the early postoperative period. The peak systolic velocity in the interpolar artery showed a significant difference between control and graft dysfunction groups (P < .001) as well as between ATN and AR (P = .019). Resistive indices and SWE did not show significant differences. Ratios of the time to peak showed a significant difference between control and graft dysfunction groups (P < .05). The rise time and fall time of the large subcapsular region of interest and the rise time ratio were significantly different between ATN and AR (P = .03).

CONCLUSIONS

Contrast-enhanced ultrasound can be used to diagnose parenchymal causes of early graft dysfunction with reasonable diagnostic accuracy.

Added Benefit and Risk of an Additional Biopsy or Targeting With Contrast-Enhanced Ultrasound for Patients With Renal Transplants

OBJECTIVES

To determine whether renal transplant diagnoses substantially change when 2 biopsy sites are chosen and whether contrast-enhanced ultrasound (CEUS) has value for targeting the second site.

METHODS

We prospectively enrolled 40 patients undergoing ultrasound-guided renal transplant biopsy within 2 years of transplant: 20, surveillance; and 20, for cause. A CEUS examination was performed to identify cortical regions with subjectively altered flow. One biopsy was performed at the operator-preferred (primary) site regardless of CEUS findings. Another biopsy was done at a second location, either targeted to an area in which CEUS perfusion findings differed from the primary site (targeted) or at a random location (secondary) if no other area differed. Specimens were randomly labeled A or B; pathologists were blinded to the CEUS result and biopsy location. Location-specific CEUS assessments were recorded. Pathologic results were compared, including acute and chronic Banff scores and any new findings from the targeted or secondary biopsy.

RESULTS

Forty patients were enrolled between January 2016 and December 2018. No location-specific pathologic differences correlated with differences in CEUS assessments. The second biopsy provided additional information that changed management in 4 of 40 patients (10.0% [95% confidence interval, 2.8%-23.7%]). Major bleeding complications occurred in 3 of 40 (7.5%) patients.

CONCLUSIONS

Contrast-enhanced ultrasound targeting was not useful. Major bleeding complications were higher than expected, possibly due to the additional biopsy away from the operator-preferred location. Obtaining a second renal transplant biopsy from a substantially different area than the initial operator-preferred location provided additional clinically useful information in 10% of patients.

B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation

OBJECTIVE

 To compare B-flow sonography (BFS) with color Doppler sonography (CDS) for imaging of kidney transplant vascularization in children.

PATIENTS AND METHODS

 All children receiving a kidney transplantation who underwent a protocol-based ultrasound examination (Loqiq 9, GE Medical Systems, Milwaukee, WI, USA) using the BFS and CDS technique with equal settings and probe position between January 2013 and January 2016 were retrospectively assessed (n = 40). The obtained datasets were visually graded according to the following criteria: (I) delineation of the renal vascular tree (Grade 1 - clear demarcation of interlobar, together with arcuate and interlobular vessels; Grade 2 - clear demarcation of interlobar and cortical vessels, but no distinction of interlobular from arcuate vessels; Grade 3 - only clear demarcation of interlobar vessels, Grade 4 - insufficient demarcation) (II) delineation of cortical vessel density in ventral, lateral, and dorsal part of the transplant, (III) smallest vessel-capsule distance, and (IV) maximum cortical vessel count. Comparison between methods was performed using Fisher's exact and paired sample t-tests.

RESULTS

 Applying a curved transducer (C1-6), BFS showed superior delineation of the renal vascular tree (p < 0.001), a lower vessel-capsule distance (p < 0.001), a higher cortical vessel count (p < 0.001), and a higher cortical vessel density in the superficial cortex (p = 0.01) than CDS. In the dorsal and lateral aspects of the transplant, cortical vessel density was lower with BFS (both p < 0.001). Using a linear high-resolution transducer (ML 6-15), no significant differences between the methods were found.

CONCLUSION

 Improved imaging of kidney transplant vascularization can be achieved in children by adding BFS to a standard protocol. The BFS technique is especially beneficial for overall assessment of the renal vascular tree together with the extent of cortical vascularization on curved array images.

KEY POINTS

  · Depiction of vascular tree and ventral cortical vessels is improved by BFS.. · The dorso-lateral cortex was better represented with CDS because of higher penetration.. · Additional monitoring with BFS improves the monitoring of transplant viability..

CITATION FORMAT

· Dammann E, Groth M, Schild R et al. B-Flow Sonography vs. Color Doppler Sonography for the Assessment of Vascularity in Pediatric Kidney Transplantation. Fortschr Röntgenstr 2021; 193: 49 - 60.

Current status of imaging diagnosis in the transplanted kidney. A review of the literature with a special focus on contrast-enhanced ultrasonography

Objectives

Ultrasonographic scanning is currently the most widespread imaging diagnostic procedure. The method provides real-time morphological, vascular and elastographic information in a non-invasive manner. In recent years, harmonic vascular examination has become accessible using intravenous contrast agents. In urological pathology, this procedure is used in the detection and evaluation of vascular and ischemic complications, in the classification of complex cysts according to the Bosniak system, also in the renal lesions with uncertain etiology and in acute pyelonephritis for the detection of abscesses. The contrast agent (SonoVue) is angiospecific and can be used in patients transplanted immediately after surgery without adverse effects or impaired renal function. Thus, it is desirable to be used in the nephrological pathology of the renal graft and to develop diagnostic models based on the evaluation of renal microvascularization, as well as the quantitative data resulting from the graphical representation of the specific parameters. The purpose of this review is to evaluate the current state of the literature regarding the place and role of contrast substance ultrasound in the early diagnosis of acute renal graft dysfunction and to make a differential diagnosis of this pathological entity.

Method

This review quantifies the role of contrast ultrasound in the diagnosis of acute complications of the renal graft. The research was conducted based on the databases PubMed, MedScape, Cochrane, according to the search criteria such as contrast-enhanced ultrasound + kidney transplant, “time intensity curves” + “kidney transplant”, filtered for the period 2004–2018.

Results

In the nephrological pathology of the renal graft, contrast-enhanced ultrasound is a valuable tool, superior to Doppler ultrasound in predicting the evolution of the renal graft, identifying very small early defects in renal microvascularization. A number of studies succeeded in identifying acute graft dysfunction, some of which establish its etiology - humoral rejection versus acute tubular necrosis. On the other hand, the contrast-enhanced ultrasound parameters do not have the ability to distinguish between cellular and humoral rejection.

Conclusions

If, at present, the histopathological examination is the only one that can differentiate with certainty the cause of acute renal graft dysfunction, we consider that contrast-enhanced ultrasound, as a non-invasive imaging technique, opens a favorable perspective for increasing the survival of the renal graft and decreasing the complications in the renal transplant. The combination of other ultrasound techniques, together with contrast-enhanced ultrasound, could lead to the development of new diagnostic models.

CYC1, SDHA, UQCRC1, UQCRQ, and SDHB might be important biomarkers in kidney transplant rejection

BACKGROUND

Kidney transplant rejection is considered as a vital factor of kidney transplant failure. Therefore, it's necessary to search for effective biomarkers for kidney transplant surveillance.

METHODS

In this study, we conducted time-series gene expression profiles analysis of samples from kidney transplant patients with different post-transplant days through weighted gene co-expression network analysis (WGCNA). Associations between gene co-expression modules and days post-transplant were determined through spearman rank correlation analysis. Potential kidney transplant rejection-related modules were subjected to gene functional enrichment analysis through clusterProfiler and protein-protein interaction analysis via STRING database.

RESULTS

A total of 11 gene co-expression modules were identified, and the pink module which was mainly involved in "energy derivation by oxidation of organic compounds" and "Huntington disease" showed significant correlation with the phenotypic trait "days post-transplant". CYC1, SDHA, UQCRC1, UQCRQ, and SDHB in the pink module exhibited high scores in the protein-protein interaction network analysis.

CONCLUSIONS

We reported several potential genes may be associated with the kidney transplant rejection, which should provide novel biomarkers for kidney transplant surveillance.

Demonstration of Improved Renal Congestion After Heart Failure Treatment on Renal Perfusion Imaging With Contrast-Enhanced Ultrasonography

Background: Renal congestion is a critical pathophysiological component of congestive heart failure (CHF). Methods and Results: To quantify renal congestion, contrast-enhanced ultrasonography (CEUS) was performed at baseline and after treatment in 11 CHF patients and 9 normal subjects. Based on the time-contrast intensity curve, time to peak intensity (TTP), which reflects the perfusion rate of renal parenchyma, and relative contrast intensity (RCI), an index reflecting renal blood volume, were measured. In CHF patients, TTP at baseline was significantly prolonged compared with that in controls (cortex, 10.8±3.5 vs. 4.6±1.2 s, P<0.0001; medulla, 10.6±3.0 vs. 5.1±1.6 s, P<0.0001), and RCI was lower than that in controls (cortex, -16.5±5.2 vs. -8.8±1.5 dB, P<0.0001; medulla, -22.8±5.2 vs. -14.8±2.4 dB, P<0.0001). After CHF treatment, RCI was significantly increased (cortex, -16.5±5.2 to -11.8±4.5 dB, P=0.035; medulla, -22.8±5.2 to -18.7±3.7 dB, P=0.045). TTP in the cortex decreased after treatment (10.8±3.5 to 7.6±3.1 s, P=0.032), but it was unchanged in the medulla (10.6±3.0 to 8.3±3.2 s, P=0.098). Conclusions: Renal congestion can be observed using CEUS in CHF patients.

Time-intensity curve analysis of contrast-enhanced ultrasound is unable to differentiate renal dysfunction in the early post-transplant period - a prospective study

Background

Contrast enhanced ultrasonography (CEUS) assessment of kidney allografts mainly focuses on graft rejection. However, studies on delayed graft function (DGF) without acute rejection are still lacking. The aim of this study was to build a time-intensity curve (TIC) using CEUS in non-immunological DGF to understand the utility of CEUS in early transplantation.

Methods

Twenty-eight patients in the short-term postoperative period (<14 days) were divided according to the need for dialysis (early graft function [EGF] and [DGF]) and 37 subjects with longer than 90 days follow-up were divided into creatinine tertiles. Time to peak [TTP] and rising time [RT were compared between groups.

Results

EGF and DGF were similar, except for creatinine. In comparison to the late group, medullary TTP and RT were shorter in the early group as well as the delay regarding contrast arrival in the medulla (in relation to cortex) and reaching the medullary peak (in relation to artery and cortex). In the late group, patients with renal dysfunction showed shorter temporal difference to reach medullary peak in relation to artery and cortex.

Conclusions

Although it was not possible to differentiate EGF and DGF using TIC, differences between early and late groups point to blood shunting in renal dysfunction.

Use of Intraoperative Duplex Ultrasound and Resistance Index Reduces Complications in Living Renal Donor Transplantation

BACKGROUND

The treatment of choice in end-stage renal disease is transplantation. Hemodynamic disturbances can evoke graft loss, while early ultrasound identification of vascular problems improves outcome. The aim of this study was to identify differences in postoperative complications with and without systematic intraoperative Doppler ultrasound use.

METHODS

The primary outcome was the postoperative rate of complications and the secondary aim was to find a predictive resistance index cut-off value, which would show where surgical reintervention was necessary. Over a 10-year period, 108 renal transplants were performed from living donors at our institution. In group 1 (n = 67), intraoperative duplex ultrasound and intraparenchymatous resistance index measurements assessed patients, while in group 2 (n = 41), no ultrasound was performed.

RESULTS

There were no intergroup differences in the overall postoperative complication rate or in benefit to graft or patient survival with Doppler use. However, significantly more vascular complications (10% vs 0%, P = .02) and more acute rejections (37% vs 10%) occurred in group 2 than in group 1. Therefore, an intraoperative cut-off value of the resistance index 0.5 was proposed to justify immediate surgical revision.

CONCLUSIONS

This is the first report demonstrating benefits of systematic intraoperative Doppler ultrasound on postoperative complications in renal transplantation from living donors. Our results support surgical revision with a resistance index <0.5.

Vascular rejection in renal transplant: Diagnostic value of contrast-enhanced ultrasound (CEUS) compared to biopsy

BACKGROUND

Despite of the more potent immunosuppressive medication, vascular rejection is still a major issue after renal transplantation. Renal biopsy is the gold standard diagnostic to evaluate acute and chronic allograft rejection. As it is an invasive diagnostic there is the risk of complications like haematoma, arteriovenous fistulas, active bleeding or infection. Contrast-enhanced ultrasound is a non-invasive imaging modality that allows visualising renal transplant perfusion.

OBJECTIVE

To analyse the sensitivity and specificity of contrast-enhanced ultrasound (CEUS) compared to biopsy as gold standard in diagnosing vascular rejection in renal transplant patients.

METHODS

A total of 57 renal transplant recipients with poor renal allograft function with initial diagnostic imaging between 2006 and 2017 were included in the study. Clinical data and imaging studies were analysed retrospectively. The diagnostic accuracy of CEUS in diagnosing vascular rejection of the renal transplant was compared to renal biopsy as gold standard. Out of 57 patients 7 patients showed signs of vascular rejection in biopsy. In 6 out of these 7 patients CEUS described irregularities in renal perfusion suspicious of vascular rejection.

RESULTS

CEUS showed a sensitivity of 85.7%, a specificity of 100%, a positive predictive value (PPV) of 100%, and a negative predictive value (NPV) of 98.0%.

CONCLUSIONS

CEUS is a safe, non-nephrotoxic imaging modality for the initial imaging of renal transplant recipients with elevated kidney function parameters suspicious of vascular rejection. Compared to renal biopsy as gold standard CEUS shows a high specificity and PPV in detecting signs of vascular rejection. Since sub-types of vascular rejection with cellular and humoral components with greater risk for allograft loss have been described renal biopsy is inevitable in these cases.

The Usefulness of Contrast-Enhanced Ultrasound in the Assessment of Early Kidney Transplant Function and Complications

OBJECTIVES

The routine diagnostic method for assessment of renal graft dysfunction is Doppler ultrasound. However, contrast-enhanced ultrasound (CEUS) may provide more information about parenchymal flow and vascular status of kidney allografts. The aim of the study was to assess the effectiveness of CEUS in the immediate post-transplant period, focusing on acute vascular complications. A brief review of available literature and a report of our initial experience is made.

MATERIAL AND METHODS

15 kidney transplant (KT) cases with clinical suspicion of acute surgical complication were assessed with CEUS and conventional Doppler ultrasound (US). In addition, bibliographic review was conducted through PubMed, Embase, and ClinicalKey databases.

RESULTS

10% of KT underwent CEUS, useful for detecting vascular complication or cortical necrosis in 4 (26%) and exclude them in 74%. Grafts with acute vascular complications have a delayed contrast-enhancement with peak intensity lower than normal kidneys. Perfusion defects can be clearly observed and the imaging of cortical necrosis is pathognomonic.

CONCLUSIONS

CEUS is a useful tool in the characterization of renal graft dysfunction with special interest on acute vascular complications after renal transplant. It is a feasible technique for quantitative analysis of kidney perfusion, which provides information on renal tissue microcirculation and regional parenchymal flow. Exploration could be done by a urologist at the patient's bedside while avoiding iodinated contrast.

The Natural History of Kidney Graft Cortical Microcirculation Determined by Real-Time Contrast-Enhanced Sonography (RT-CES)

Background

Kidney transplantation is the therapy of choice for end-stage kidney disease. Graft’s life span is shorter than expected due in part to the delayed diagnosis of various complications, specifically those related to silent progression. It is recognized that serum creatinine levels and proteinuria are poor markers of mild kidney lesions, which results in delayed clinical information. There are many investigation looking for early markers of graft damage. Decreasing kidney graft cortical microcirculation has been related to poor prognosis in kidney transplantation. Cortical capillary blood flow (CCBF) can be measured by real-time contrast-enhanced sonography (RT-CES). Our aim was to describe the natural history of CCBF over time under diverse conditions of kidney transplantation, to explore the influence of donor conditions and recipient events, and to determine the capacity of CCBF for predicting renal function in medium term.

Patients and Methods

RT-CES was performed in 79 consecutive kidney transplant recipients during the first year under regular clinical practice. Cortical capillary blood flow was measured. Clinical variables were analyzed. The influence of CCBF has been determined by univariate and multivariate analysis using mixed regression models based on sequential measurements for each patient over time. We used a first-order autoregression model as the structure of the covariation between measures. The post-hoc comparisons were considered using the Bonferroni correction.

Results

The CCBF values varied significantly over the study periods and were significantly lower at 48 h and day 7. Brain-death donor age and CCBF levels showed an inverse relationship (r: -0.62, p<0.001). Living donors showed higher mean CCBF levels than brain-death donors at each point in the study. These significant differences persisted at month 12 (54.5 ± 28.2 vs 33.7 ± 30 dB/sec, living vs brain-death donor, respectively, p = 0.004) despite similar serum creatinine levels (1.5 ± 0.3 and 1.5 ± 0.5 mg/dL). A sole rejection episode was associated with lower overall CCBF values over the first year. CCBF defined better than level of serum creatinine the graft function status at medium-term.

Conclusion

RT-CES is a non-invasive tool that can quantify and iteratively estimate cortical microcirculation. We have described the natural history of cortical capillary blood flow under regular clinical conditions.

Contrast-enhanced ultrasound of both kidneys in healthy, non-anaesthetized cats

Background

Changes in perfusion are considered to play a key role in the pathophysiology of renal disease. Contrast-enhanced ultrasound (CEUS) has shown a promising diagnostic imaging technique to non-invasively and repetitively quantify tissue perfusion. Examination protocols have varied between studies regarding US equipment, quantification software, the use of sedation or anaesthesia, and animals. The purpose of the present study was, to assess the feasibility of a standardized CEUS protocol for perfusion analysis of both kidneys in nine healthy, non-anaesthetized cats.

Results

CEUS was fairly tolerable for all but one cat. In 6/18 kidneys (2 left, 4 right), a second contrast medium injection was needed due to motion artifacts. Perfusion variables such as peak intensity (PI), wash-in slope (WI_S), wash-out slope (WO_S) and mean transit time (MTT) did not significantly differ between left and right renal cortex and medulla nor between the cranial and caudal renal cortex within each kidney. In contrast, for all kidneys, mean PI, WI_S, and MTT were significantly higher in the cortex than in the medulla (P = 0.001, 0.012 and <0.001, respectively).

Conclusions

The herein reported CEUS protocol and the perfusion measurements may serve as a baseline protocol and normal reference values for the evaluation of feline patients. However, the protocol and results may be of limited value in uncooperative animals.

Effects of high-fat diet and losartan on renal cortical blood flow using contrast ultrasound imaging

Obesity-related kidney disease occurs as a result of complex interactions between metabolic and hemodynamic effects. Changes in microvascular perfusion may play a major role in kidney disease; however, these changes are difficult to assess in vivo. Here, we used perfusion ultrasound imaging to evaluate cortical blood flow in a mouse model of high-fat diet-induced kidney disease. C57BL/6J mice were randomized to a standard diet (STD) or a high-fat diet (HFD) for 30 wk and then treated either with losartan or a placebo for an additional 6 wk. Noninvasive ultrasound perfusion imaging of the kidney was performed during infusion of a microbubble contrast agent. Blood flow within the microvasculature of the renal cortex and medulla was derived from imaging data. An increase in the time required to achieve full cortical perfusion was observed for HFD mice relative to STD. This was reversed following treatment with losartan. These data were concurrent with an increased glomerular filtration rate in HFD mice compared with STD- or HFD-losartan-treated mice. Losartan treatment also abrogated fibro-inflammatory disease, assessed by markers at the protein and messenger level. Finally, a reduction in capillary density was found in HFD mice, and this was reversed upon losartan treatment. This suggests that alterations in vascular density may be responsible for the elevated perfusion time observed by imaging. These data demonstrate that ultrasound contrast imaging is a robust and sensitive method for evaluating changes in renal microvascular perfusion and that cortical perfusion time may be a useful parameter for evaluating obesity-related renal disease.

Use of quantitative contrast-enhanced ultrasonography to detect diffuse renal changes in Beagles with iatrogenic hypercortisolism

OBJECTIVE

To determine the feasibility of quantitative contrast-enhanced ultrasonography (CEUS) for detection of changes in renal blood flow in dogs before and after hydrocortisone administration.

ANIMALS

11 Beagles.

PROCEDURE

Dogs were randomly assigned to 2 treatment groups: oral administration of hydrocortisone (9.6 mg/kg; n = 6) or a placebo (5; control group) twice a day for 4 months, after which the dose was tapered until treatment cessation at 6 months. Before treatment began and at 1, 4, and 6 months after, CEUS of the left kidney was performed by IV injection of ultrasonography microbubbles. Images were digitized, and time-intensity curves were generated from regions of interest in the renal cortex and medulla. Changes in blood flow were determined as measured via contrast agent (baseline [background] intensity, peak intensity, area under the curve, arrival time of contrast agent, time-to-peak intensity, and speed of contrast agent transport).

RESULTS

Significant increases in peak intensity, compared with that in control dogs, were observed in the renal cortex and medulla of hydrocortisone-treated dogs 1 and 4 months after treatment began. Baseline intensity changed similarly. A significant increase from control values was also apparent in area under the curve for the renal cortex 4 months after hydrocortisone treatment began and in the renal medulla 1 and 4 months after treatment began. A significant time effect with typical time course was observed, corresponding with the period during which hydrocortisone was administered. No difference was evident in the other variables between treated and control dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Quantitative CEUS allowed detection of differences in certain markers of renal blood flow between dogs treated orally with and without hydrocortisone. Additional studies are needed to investigate the usefulness of quantitative CEUS in the diagnosis of diffuse renal lesions.

Ultrasonographic features of kidney transplants and their complications: an imaging review

Renal transplantation is the treatment of choice for managing patients with end-stage kidney disease. Being submitted to a very serious surgical procedure, renal transplant recipients can only benefit from follow-up imaging and monitoring strategies. Ultrasound is considered as the principal imaging test in the evaluation of renal transplants. It is an easily applied bedside examination that can detect possible complications and guide further imaging or intervention. In this imaging review, we present essential information regarding the sonographic features of healthy renal transplants, detailing the surgical technique and how it affects the sonoanatomy. We focus on various complications that occur following renal transplantation and their sonographic features by reviewing pertinent literature sources and our own extensive imaging archives.

Biological modulation of renal ischemia-reperfusion injury

PURPOSE OF REVIEW

Biological modulation of renal ischemia-reperfusion injury holds the potential to reduce the incidence of early graft dysfunction and to safely expand the donor pool with kidneys that have suffered prolonged ischemic injury before organ recovery.

RECENT FINDINGS

In the current review, we will discuss clinical studies that compare kidney transplant recipients with and without early graft dysfunction in order to elucidate the pathophysiology of ischemic acute allograft injury. We will specifically review the mechanisms leading to depression of the glomerular filtration rate and activation of the innate immune system in response to tissue injury.

SUMMARY

We conclude that the pathophysiology of delayed graft function after kidney transplantation is complex and shares broad similarity with rodent models of ischemic acute kidney injury. Given the lack of specific therapies to prevent delayed graft function in transplant recipients, comprehensive efforts should be initiated to translate the promising findings obtained in small animal models into clinical interventions that attenuate ischemic acute kidney injury after transplantation.

Evaluation of renal microcirculation by contrast-enhanced ultrasound with Sonazoid as a contrast agent

Chronic kidney disease (CKD) is a major and serious risk factor for cardiovascular disease (CVD). Continuous hypoxia due to hypoperfusion in peritubular capillaries is one of the factors aggravating CKD, but evaluation of perfusion in this region is difficult using clinically available imaging methods. Since the second-generation ultrasound contrast agent Sonazoid has a stable shell, it enables visualization of the renal vasculature for a long period of time. We therefore evaluated changes in contrast-enhanced ultrasound (CEUS) imaging with Sonazoid in CKD patients.Sonazoid was used in 85 CKD patients and 5 control subjects, and images were recorded for 10 minutes. Time-intensity curves were generated from the images of 62 time points in both cortex and medulla.In control samples, contrast enhancement spread from the hilar portion to the periphery along the direction of arterial flow, and renal cortex and medulla were then enhanced in sequence. Enhancement was maximal soon after, then gradually decreased, but was still visible at 600 seconds. In CKD patients, renal contrast enhancement was attenuated in both cortex and medulla. On time-intensity curves, the attenuation of enhancement was composed of delayed rising, reduction of peak, and acceleration of decay in both cortex and medulla with progression of renal dysfunction. No side effects of the contrast agent were observed in any subjects.The attenuation of renal contrast enhancement observed in CKD patients appears to reflect disturbance of perfusion in peritubular capillaries. CEUS with Sonazoid is a useful and safe means of visualizing the renal microvasculature.

Ultrasonography in kidney transplantation: values and new developments

Renal transplant is performed on patients with end-stage renal disease. Gray-scale renal sonography combined with color Doppler has become the main noninvasive imaging method for evaluating a kidney transplant, as it provides information about the kidney anatomy and its vascular flow. In this article, we discuss the utility of sonography in renal transplants and describe the ultrasound findings in early and chronic graft pathology. Also, we explain new developments in ultrasound imaging with contrast media and its utility in renal transplantation, proposing that contrast-enhanced sonography be incorporated as a method to evaluate graft status because of its capability to evaluate cortical capillary blood flow.

Motion corrected cadence CPS ultrasound for quantifying response to vasoactive drugs in a rat kidney model

OBJECTIVE

To establish the ability of contrast-enhanced motion corrected cadence pulse sequencing (CPS) to detect changes in renal blood flow induced by vasoactive substances in rats.

METHODS

Ultrasound contrast media was administered as a constant rate infusion into a phantom at a known rate and CPS data acquired. Rats were anesthetized and predrug CPS estimates of replenishment rate were made for the right kidney. Real-time motion correction was applied, and parametric images were generated from the CPS data. Group 1 rats (n = 7) were administered a vasodilator and group 2 rats (n = 3) were administered a vasoconstrictor. The CPS imaging of the kidney was repeated after ample time for drug effects to occur.

RESULTS

Contrast CPS accurately estimated flow velocity in the phantom model. In addition, CPS defined statistically significant differences between pre- and postdrug blood flow in the renal medulla (vasodilator, P < .01; vasoconstrictor, P < .0001) and cortex (vasoconstrictor, P < .0001).

CONCLUSIONS

We conclude that motion-corrected CPS ultrasound provides real-time quantification of renal blood flow alterations and may prove useful for the assessment of blood flow in transplanted kidneys.

Non-invasive imaging of acute renal allograft rejection in rats using small animal F-FDG-PET

BACKGROUND

At present, renal grafts are the most common solid organ transplants world-wide. Given the importance of renal transplantation and the limitation of available donor kidneys, detailed analysis of factors that affect transplant survival are important. Despite the introduction of new and effective immunosuppressive drugs, acute cellular graft rejection (AR) is still a major risk for graft survival. Nowadays, AR can only be definitively by renal biopsy. However, biopsies carry a risk of renal transplant injury and loss. Most important, they can not be performed in patients taking anticoagulant drugs.

METHODOLOGY/PRINCIPAL FINDINGS

We present a non-invasive, entirely image-based method to assess AR in an allogeneic rat renal transplantation model using small animal positron emission tomography (PET) and (18)F-fluorodeoxyglucose (FDG). 3 h after i.v. injection of 30 MBq FDG into adult uni-nephrectomized, allogeneically transplanted rats, tissue radioactivity of renal parenchyma was assessed in vivo by a small animal PET-scanner (post operative day (POD) 1,2,4, and 7) and post mortem dissection. The mean radioactivity (cps/mm(3) tissue) as well as the percent injected dose (%ID) was compared between graft and native reference kidney. Results were confirmed by histological and autoradiographic analysis. Healthy rats, rats with acute CSA nephrotoxicity, with acute tubular necrosis, and syngeneically transplanted rats served as controls. FDG-uptake was significantly elevated only in allogeneic grafts from POD 1 on when compared to the native kidney (%ID graft POD 1: 0.54+/-0.06; POD 2: 0.58+/-0.12; POD 4: 0.81+/-0.06; POD 7: 0.77+/-0.1; CTR: 0.22+/-0.01, n = 3-28). Renal FDG-uptake in vivo correlated with the results obtained by micro-autoradiography and the degree of inflammatory infiltrates observed in histology.

CONCLUSIONS/SIGNIFICANCE

We propose that graft FDG-PET imaging is a new option to non-invasively, specifically, early detect, and follow-up acute renal rejection. This method is potentially useful to improve post-transplant rejection monitoring.

Quantitative contrast enhanced ultrasound of the liver for time intensity curves-Reliability and potential sources of errors

INTRODUCTION

Time intensity curves for real-time contrast enhanced low MI ultrasound is a promising technique since it adds objective data to the more subjective conventional contrast enhanced technique. Current developments showed that the amount of uptake in modern targeted therapy strategies correlates with therapy response. Nevertheless no basic research has been done concerning the reliability and validity of the method.

PATIENTS AND METHODS

Videos sequences of 31 consecutive patients for at least 60s were recorded. Parameters analysed: area under the curve, maximum intensity, mean transit time, perfusion index, time to peak, rise time. The influence of depth, lateral shift as well as size and shape of the region of interest was analysed.

RESULTS

The parameters time to peak and rise time showed a good stability in different depths. Overall there was a variation >50% for all other parameters. Mean transit time, time to peak and rise time were stable from 3 to 10cm depths, whereas all other parameters showed only satisfying results at 4-6cm. Time to peak and rise time were stable as well against lateral shifting whereas all other parameters had again variations over 50%. Size and shape of the region of interest did not influence the results.

DISCUSSION

(1) It is important to compare regions of interest, e.g. in a tumour vs. representative parenchyma in the same depths. (2) Time intensity curves should not be analysed in a depth of less than 4cm. (3) The parameters area under the curve, perfusion index and maximum intensity should not be analysed in a depth more than 6cm. (4) Size and shape of a region of interest in liver parenchyma do not affect time intensity curves.

Renal transplant rejection markers

Acute rejection is one of the key factors which determine long-term graft function and survival in renal transplant patients. Timely detection and treatment of rejection is therefore, an important goal in the post-transplant surveillance. The standard care with serum creatinine measurements and biopsy upon allograft dysfunction implies that acute rejection is detected in an advanced stage. Therefore, non-invasive monitoring for acute rejection by markers in blood and urine has been tried over the past decades. This review describes the requirements that should be met by non-invasive markers. The experience with single biomarkers and with newer approaches--mRNA expression analysis, metabolomics, and proteomics--will be discussed, including future directions of necessary research.